1.Field of the Invention
The present invention relates to a central processing unit (CPU) speed control system and, more particularly, to a task specific control system for enabling the CPU to be clocked at varying speeds corresponding to the particular task being executed.
2.Description of the Related Art
Various CPU speed control systems are known for enabling the clock speed of a CPU and/or various system buses in a personal computer (PC) to be reduced during periods of inactivity. Such CPU speed control systems generally result in less energy consumption by desktop type PCS whose usual power source is about 120 volt, 60 Hertz (Hz) wall connection. For example, substantial savings in electrical power consumption are possible due to the large numbers of computers which are left on for extended periods of time, even when not being actively used. Similarly, CPU speed control systems also result in more efficient use of battery power in portable PCS, resulting in extended battery life or smaller batteries.
Power consumption management systems, present in portable and desktop computers, traditionally rely upon hardware timers which, upon expiration, turn off or reduce power to various systems components. For example, the current "Green Computer" energy saving standards allow devices to be powered off after periods of inactivity. In particular, monitors are shut down, disks stop spinning, and eventually the entire system is shut down in an orderly fashion.
Power saving features have become increasingly important over the past few years because of the dramatic increase in processor clock speeds. In particular, as clock speeds increase, systems having faster microprocessors use significantly more power than systems with slower clock speed microprocessors. For example, a 266 MHz Intel Pentium II processor may draw three times the current of a 75 MHz classic Pentium processor. Furthermore, not only the CPU, but often the entire system bus operates off of a single clock, so all of the chip sets, including I/O controllers, memory, and other components draw higher currents at higher clock speeds than sometimes necessary for efficient use of the computer system.
CPU clock control systems have been developed. Examples of such systems are disclosed in U.S. Pat. Nos.: 5,546,568; 5,504,910; 5,754,869; 4,819,164; 5,490,059; and 5,218,704. Such CPU speed control systems normally include a CPU and a frequency synthesizer for supplying the CPU with an operating clock which may be operated at different frequencies. These CPU clock control systems vary the clock speed of the frequency synthesizer according to a number of different considerations. Such considerations may include, for example, the amount and frequency of system activity, the temperature of the CPU, and whether the computer system is receiving keyboard or other input. Unfortunately, such CPU speed control systems rely on prophylactic methods of speed control wherein the CPU is stopped or slowed down based on particular criteria. For example, the CPU speed may be varied depending on the amount of system activity, the temperature of the CPU or whether the computer system is sensing any input. However, CPU clock speeds are generally not adaptable to task specific microprocessor clock speed requirements. Thus, there is a need for a CPU speed control system which enables the CPU input clock to be varied in accordance with the particular task or application being executed.